The invention relates to and has among its objects the provision of a novel method and apparatus for providing in combination visual and olfactory stimuli to fruit flies to rapidly assess behavioral responses of the flies to sample test chemicals.
Tephritid fruit flies such as the Mediterranean fruit fly [Ceratitis capitata (Widemann)] commonly referred to as the medfly, Oriental fluit fly (Dacus dorsalis Hendel), melon fly (D. cucurbitae Coquillet), Caribbean fruit fly [Anastepha suspensa (Loew)], olive fruit fly (D. oleae Gmelin), and Mexican fruit fly [A. ludens (Loew)] are among the worst pests of stonefruit and citrus fuits and vegetables and present a major threat to fruit and vegetable production. In the case of the medfly, although infestations of these flies are primarily in subtropical regions of the continent and in Hawaii, periodic invasions onto the mainland United States have resulted in great economic loss due to crop losses and costs to eradicate the pest.
Chemicals which modify the behavior of these flies, particularly those which elicit an approaching or departing response or nullify one of these responses, are important in the control of these pests. Various activities may be elicited by behavior-modifying chemicals. For example, a compound may act as an attractant, that is, produce a significant increase in number of flies attracted over those attracted by unbaited traps but that does not act as a sex attractant; sex attractant, that is, a compound that produces increased response in flies of one sex and also elicits additional responses similar to those evoked by natural sex peromonal emmissions; aggregant, that is, a compound that attracts flies of both sexes and evokes responses similar to those of natural pheromonal emissions; inhibitor, that is, a compound that reduces the number of flies attracted when exposed in a trap baited with an attractant, a phermonal extract, or live flies; disruptant, that is, a compound that interferes with the ability of insects to locate mates when the compound is disseminated throughout an area; synergist, that is, a compound that, though not attractive in itself, causes a significant increase in number of insects attracted when exposed to an attractant; and a repellant, that is, a compound which repells flies when exposed along with attractant compounds or material.
To be of any value, the behavioral response of such chemicals must be demonstrable in the normal habitat of the insect. This is particularly true in a highly evolved acalyptrate dipteran group such as tephritid fruit flies which have complex chemical communication mechanisms. Laboratory studies of fruit fly response to test chemicals have been found, in some cases, to be completely contradictory to responses by the fly in the field. For example, when the attractant compound methyl (E)-6-nonenoate (MEN) was tested in the laboratory, it attracted female medflies; in contrast, MEN was solely attractive to male medflies in the field.
Another important criteria in the field testing of chemicals which elicit a behavioral response of fruit flies is the ability to observe responses such as courtship, mating, feeding, defense of territory, and other behavioral patterns, in addition to merely quantifying numbers of flies attracted or captured. This is particularly important in the study of tephritid fruit flies because many of these flies, notably those of economic importance, naturally initiate aggregations by males where attraction, courtship, and mating with female flies are performed. Distant chemical communication is accomplished from leks, i.e., territories within host plant communities where the intricate male displays and signaling are conducted, often away from ovipositional sites subsequently selected by females.
Presently, no method or apparatus exists for the rapid assessment in the field of fruit fly response to behavior-modifying chemicals. Devices to measure olfactory response of fruit flies in the laboratory are well known. These include small to walk-in sized cage-type olfactometers in which traps containing candidate compounds are suspended from a rotating motor-driven wheel to provide rotational presentation of test materials or which provide wind-tunnel effects. These devices have the problems that laboratory response may not be indicative of field response, that artifacts may be introduced, and that primary measurement is number of flies trapped or contained. Observations of numbers of test chemicals in the trephritid natural habitat is impractical because of the time required to locate difficult to find mating sites for testing. Conventional devices to test behavior-modifying chemicals in the field comprise traps which measure the number of flies trapped or contained. While these devices are useful for detecting, monitoring, or mass-trapping flies, other responses such as mating, courtship, and the like are not elicited with these traps. Additionally, conventional traps have to be distributed over a large area and replicated several times to obtain a meaningful response and thus require weeks of time and manpower.
Two-dimensional visual cues such as host plant foliage pressed between plexiglass sheets, a tree-shaped pattern drawn on plywood, and colors and shapes similuating host fruit contrasts have been tested against tephritids to provide insight into visual stimuli; however, no method or device has fulfilled the need for a rapid way to assess behavioral responses such as courtship, mating, feeding, and the like of fruit flies in the field in response to behavior-modifying chemicals.